This invention relates to processes for producing hydrogen peroxide, and more particularly to improvements in the cyclic process for the production of hydrogen peroxide.
Conventional cyclic processes for the production of hydrogen peroxide involve hydrogenating one or more alkylanthraquinones dissolved in a water-immiscible solvent, so as to convert them into alkylhydroanthraquinones; subsequently treating the reaction medium with a gas containing oxygen so as to form hydrogen peroxide while regenerating the starting alkylanthraquinones; and finally extracting the hydrogen peroxide from the solution of quinones using water, before recycling the solution of quinones into the hydrogenation step.
In descriptions of processes of this kind, the term "anthraquinones" is generally used to mean so-called "true" anthraquinones with aliphatic substituents, and hydroanthraquinones, such as the tetrahydrogenated derivatives of these anthraquinones.
In these recycling processes, it is well known that, if the active intermediates have been introduced into the reaction cycle in the form of a true anthraquinone, the latter is progressively converted into the tetrahydrogenated form in the course of the successive operation of recycling of the solution.
The proportion of the tetrahydrogenated form reached is variable and depends on the working conditions at every stage of the manufacturing process.
It is also known, in fact, that other undesirable reactions convert the active intermediates into inactive products, some of which can be reconverted into active intermediate. This reconversion can be effected by various processes within the cycle or outside it.
It should be noted that these processes are themselves liable to affect the proportion of tetrahydroanthraquinone, and therefore the proportion of true anthraquinones and the tetrahydrogenated derivatives thereof depends on all the process conditions.
In Oxysynthese French Pat. No. 1,498,406 relating to a process similar to that described above, a mixture of anthraquinones containing 2-ethylanthraquinone and 2-ethyl-5,6,7,8-tetrahydroanthraquinone, referred to herein as "EAQ" and "H.sub.4 EAQ", respectively, is used. In the French patent the working conditions are adjusted so that the proportion of H.sub.4 EAQ is about 90% of the mixture of the two anthraquinones. The conversion rate on hydrogenation is approximately 90%, and the solution contains a substantial proportion of inactive products, which are derived from the two anthraquinones used. This proportion, which is preferably greater than 150 g/L, makes it possible to achieve productivity levels exceeding 13 g of H.sub.2 O.sub.2 /L.
The presence of these inactive products increases the solubility of the anthraquinones and hydroanthraquinones and consequently the equivalent concentration of hydrogen peroxide in the solution. However, although these products play a useful part, an accumulation of them beyond the selected limit constitutes a loss of the active intermediate, thus involving some considerable expense.